Carburetor



March 23, 1955 M. c. BROWN 3,74,732

CARBURETOR Filed Sept. 28. 1962 fr Y r 33 374745 4q QHSS INVENTOR.MORRIS c. BRO N United States Patent O 3,174,732 CARBURETOR Morris C.Brown, St. Louis, Mo., assigner to ACF Industries, Incorporated, New`iZork, NSY., a corporation of New Jersey Filed Sept. 28, 1962, Ser. No.226,950 3 Claims. (Cl. 251-69) This invention relates to carburetors,and more particularly to carburetors of the diaphragm type, by which ismeant a carburetor as to which delivery of fuel to a fuel chamber of thecarburetor is controlled by a diaphragm, as distinguished frombeingcontrolled by a float.

The invention is particularly applicable to a small dia phragmetypecarburetor for small internal combustion engines such as are used inportable tools (chain saws, for example), in lawn mowers, smallautomotive vehicles such as are sometimes called go-carts, etc.

A diaphragm-type carburetor generally comprises a mixture conduit inwhich fuel is mixed with air for delivery to the intake manifold of anengine, a fuel chamber closed by a diaphragm and communicating through ano2- zle with the mixture conduit for delivery of fuel thereto, andvalve means controlled by the diaphragm for controlling delivery of fuelfrom a fuel tank to the fuel chamber. An air filter is provided forcleaning air entering the mixture conduit. The mixture conduit is formedwith a restriction, .e.g., a venturi. With the engine in operation, airiiows through the mixture conduit, a pressure drop occurs across theventuri (meaning that there is a partial vacuum in the venturi), andpressure on the outside of the diaphragm causes the diaphragm to flexinward and effect delivery of fuel through the nozzle (usually locatedat the throat of the venturi where the pressure drop is a maximum) andto effect opening lof the valve means for delivery of fuel to the fuelchamber.

A problem in prior carburetors of the class described has been controlof the diaphragm for maintenance of a balanced air and fuel ratio as theair filter becomes clogged with dirt. Use of an inside vent, whichinterconnects a diaphragm control chamber to the carburetor inlet insidethe air filter is not completely effective to maintain the air and fuelratio in balance as the air filter becomes increasingly clogged.

Accordingly, it is the principal object of this invention to provide avent system, particularly for a carburetor of the class described, ofthe full inside vent type which functions effectively to maintain apredetermined air and fuel ratio regardless of air filter clogging. ingeneral, the vent system of this invention accomplishes this result bysensing the changes caused by the air filter becoming increasinglyclogged. The invention provides a means for sensing the pressure dropacross the carburetor venturi in the mixture conduit, and subjecting thediaphragm to a pressure representing a balance of pressure drops in themixture conduit. Other objects and features will be in part apparent andin part pointed out hereinafter.

The invention accordingly comprises the constructions hereinafterdescribed, the scope of the invention being indicated in the followingclaims.

In the accompanying drawings, in which one of various possibleembodiments of the invention is illustrated,

FIG. 1 is a longitudinal section of a diaphragm-type carburetor showinga vent system of this invention;

FIG. 2 is a transverse section taken on line 2 2 of FIG. l; and

FIG. 3 is a fragmentary transverse section taken on line 3 3 of FiG. 1.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

Referring to the drawings, a carburetor constructed in accordance withthis invention, and generally designated ice 1, is shown to comprise amain body 3 formed to provide a mixture conduit 5 extending therethroughfrom one end to the other. As appears in FIG. 1, the mixture conduit 5is formed to have a cylindric throttle section or bore 7 toward one end,an intermediate restricted section 9 of venturi form, and an inletsection 11 toward its other end. The latter is generally cylindric, butwith a flat as indicated at 13. The throat (the region of smallest crosssection) of the venturi section 9 is indicated at 15. Body 3 has aflange 17 at the said one end of the mixture conduit (which constitutesits downstream end) for attaching the carburetor to the intake manifold19 of an internal combustion engine as appears in FIG. l, the flangebeing pprovided with suitable bolt holes (not shown) for receiving boltsextending from the intake manifold for this purpose.

An air filter 21 is attached in suitable manner to the body 3 at theupstream end of the mixture conduit. As appears in FIG. l, this airfilter is of a type comprising a casing 23 containing an annular filterelement 25. The hole in the center of the filter element is indicated at27. This hole is aligned with the mixture conduit 5. Air enters thefilter peripherally, as indicated by the arrows in FIG. 1, tiows throughthe filter element to the hole 27, and thence through the mixtureconduit during the operation of the engine.

Body 3 is formed with a shallow recess 29 of circular outline in oneside thereof (its bottom side as appears in the drawings). This recess,which constitutes a fuel charnber, has its center generally in the planeof the venturi throat 15, and is closed by a flexible diaphragm 31 (madeof fuel-resistant synthetic rubber, for example). The margin of thediaphragm 31 is clamped against the body by a cover 33, fastened to thebody by screws as indicated at 35. Cover 33 is recessed as indicated at37 to provide a diaphragm control chamber on the outside of thediaphragm. A gasket 39 is interposed between the margin of the diaphragmand the cover to seal chamber 37 from the outside atmosphere. Thecentral portion of the diaphragm is maintained substantially flat andrigid by a pair of flat spoked wheel-like backing members 41 and 43lying on opposite faces of the diaphragm, and held in assembly with thediaphragm by a rivet 4S having its shank entered in a center hole in thediaphragm and center holes in members 41 and 43. The inner end head ofthe rivet is in the form of a button 47 for engagement by one end of avalve-actuating lever 49.

Fuel is adapted to be supplied to fuel chamber 29 from a fuel tank 51 asshown in FIG. 2, the carburetor including fuel pump means as generallyindicated at 53 for pumping fuel to chamber 29, and a needle valve 55controlled by the aforementioned lever 49 for controlling delivery offuel to the fuel chamber 29. For purposes of providing the fuel pumpmeans, body 3 is formed with a shallow circular recess S7 constituting apulsation chamber in the side thereof (its top side as shown) oppositethe chamber 29 and, laterally offset from this recess 57, with anannular cavity 59 surrounding a boss 61. Recess 57 and cavity 59 areclosed by a exible pump diaphragm 63 (made of fuel-resistant syntheticrubber, for example) clamped against the body all around the recess 57and the cavity 69 by a pump cap 65. The latter is fastened to the bodyby screws as indicated at 67. It has a recess 69 constituting a pumpingchamber on the opposite side of the diaphragm from recess or pulsationchamber S7.

The pump cap is formed with an upwardly extending boss 71 having ahorizontal hole 73 extending inward from one side of the carburetor anda vertical hole '75 extending down from the inner end of hole 73 to thepumping chamber 69. Holes 73 and 75 together constitute a fuel inletpassage. A nipple 77 pressed in the end of hole 73 is adapted forconnection of a fuel line 78 leading from the fuel tank 51. The pump capis also formed with an outlet dome 79 which opens upward from pumpingchamber 57 alongsideY hole 75, from which there is an inclined outletpassage 81 to a cavity 83 in the pump cap on the opposite side of pumpdiaphragm '63 from the annular cavity 59. From the pulsation chamber 57there is a passage 85 through the body 3 of the carburetor forcommunication between the intake manifold 19 and pulsation chamber 57. Areed valve (not shown) normally closes conduit and passage 85 during theexhaust cycle of the engine. Pressure pulsations inthe intake manifoldare transmitted through passage 85 to chamber 57 and cause flexing ofpump diaphragm 63. Fuel is thereby drawn into pumping chamber 69 fromtank 51V through inlet passage 73, 75 on downstrokes of diaphragm 63 andforced out of pumping chamber 69 on upstrokes of the diaphragm 63through outlet chamber 79 and outlet pasisage 81 under control ofapper-type inlet and outlet check valves'87 and 89. These are formed byC-shaped cuts in av valve member consisting of a disk 91 offuelresistant synthetic rubber, for example, held in place by a retainer93. The inlet iiapper valve 87 flexes down to open when diaphragm 63flexes down (outlet check S9 then being closed), and iiexes to close offthe lower end of hole 75 when diaphragm 63 flexes up. The outlet flappervalve 89 iiexes up to open when diaphragm 63 flexes up (inlet check 87then being closed) and iiexes down to close off on outlet hole 94 inretainer 93 when diaphragm 63 exes down.

Body 3 has a cylindric pocket 95 extending up from fuel chamber 29alongside the mixture conduit 5, this pocket being aligned with theaforementioned boss 61. A passage 97 extends down through the boss`61and the body 3 to the upper end of the recess 95. A flanged tubularfitting 96 pressed in the upper end of passage 97 holds down the pumpdiaphragm'63. A tubular cylindric needle valve body 99 is received inrecess 95, being held in recess 95 by a screw-threaded fitting 191threaded in the lower end of this recess. The needle valve body'99 hasan upper end head 103 provided with anl axial bore 105 forming acontinuation of passage 97. A resilient valve seat 107, consisting of adisk of fuel-resistant synthetic rubber, Vfor example, having a centerhole, is yretained at the bottom ofthe head 103 as by a ring 109 pressedinto the needle valve body. The latter has a reduced extension 111 fromthe upper end of head 93 having an annular groove receiving an O-ring113 for sealing against body 3 at the upper end of recess 95.

Fitting 101 has a central opening slidably receiving the stern of needlevalve 55, the latter having a tapered nose 115 at its upper end forengagement with valve seat 107. The opening in the fitting is formed forflow of fuel therethrough around the stem of the needle valve. A coilcompression spring 117 surrounding the Vneedle valve reacts from thelower end of retainer 101 againsta collar 119 on the needle valve tobias the needle valve to a closed position engaging the valve seat 107.The needle valve Y has anannular groove 121 at its lower end providing alower end head 123on the needle valve. The valve-actuating lever 49comprises a metal strip bent as .indicated at 125 .to form anupwardlytopening loop.Y Lever 49 is pivoted intermediate its ends on apivot pin 127 received in loop 125` This pin extends parallel to theaxis of the mixture conduit 5 across an upward extension 29a of the fuelchamber 29. Lever 49 thus extends laterally in respect to the carburetorand has its inner endl overlying button 47 on the control diaphragm 31.The outer end Yof the lever is forked as indicated at 129 and straddlesthe needle valve within the groove 121 above the lower end head 123 ofthe needle valve.

A throttle shaft 131 is journalled in body 3 extending laterally acrossthrottle bore 7 of the mixture conduit 5'.

4 one end. A choke shaft 137 is journalled in body 3 extending laterallyacross the inlet section 11 of mixture conduit 5. Shaft 137 carries achoke 139 constituted by a sheet metal plate, and, as will beunderstood,has an operating arm (not shown) on one end.

Body 3 is formed with a hole Y141 extending upV from fuel chamber 29 tomixture conduit 5, Vthis hole being concentric with the fuel chamber andin the plane of the venturi throat 15. It is stepped, having an enlargedlower portion 143. A nozzle is received in this hole. This nozzlecomprises a tubular element having an enlarged lower portion 147 ofoutside diameter corresponding to the diameter of the upper portion ofhole 141, this lower portion being pressed into the upper portion of thehole.

At the lower end of theV nozzle is a flange 149 which seats againstthebody 3 Varound the lower end of hole 141 for sealing the lower end ofthe hole from fuel chamber 29. The lower end of the nozzle is plugged asindicated at 151. The tip of the nozzle extends up into the venturithroat 15.

Body 3 has a cavity 155 extending up from fuel chamber 29 alongside hole141 on the side thereof opposite the needle valve pocket 95. This isintersected by a lateral horizontal hole 157 which at its inner end isin communication with the annular space around the lower portion 147 ofthe nozzle in the lower portion 143 of hole 141 via an orifice 159. Thelower portion 147 of the nozzle has ports 161 for communication fromthis annular space to the interior of the nozzle above plug 151. Cavity155, hole 157, orifice 159, the stated annular space, ports 161 and thepassage in nozzle 145 constitute the high speed fuelcircuit of thecarburetor, fuel being adapted to ow therethrough from fuel chamber 29to the mixture conduit 5 upon opening throttle 133 and resultant flow ofair through the mixture conduit. The flow is adapted to be metered by ahigh speed circuit adjusting screw 163 threaded in hole 157 and having asmall-diameter pointed-end extension 165 reaching to the orifice 159.

Downstream from hole 141, body 3 has a cavity 167 (see FIGS. `1 and 3)in the central longitudinal plane of the mixture conduit 5 extending upfrom fuel chamber 29. An idle fuel port 169 opens from the upper end ofthis cavity into the mixture conduit 5 downstream from thek closedthrottle 133. Idle air bleed holes 171 open into the upper end of thiscavity from the mixture conduit upstream from the closed throttle. Thelower end of cavity 167 is closed by a plug 173.V Body 3 has a .cavity175 extending Vup from fuel chamber 29 alongside cavity167. Cavity 175is intersected by a lateral horizontal hole 177 which at itsinner end isin communication with cavity 167 via an oriiice 179. Cavity 175, hole177, orifice 179, cavity 167 and port 169 constitute the low speed oridle fuel circuit of the carburetor, fuel being adapted to flowtherethrough from fuel chamber 29 to the mixture conduit 5, air mixingwith the fuel via ports 171. The ow of idle fuel is adapted to bemeteredby an idle adjusting screw 181 threaded in hole 177 and havingY asmall-diameter.pointed-end extension 183 reaching to the orifice 179.

Body 3 has a Ypassage 185 extending down from they mixture conduit 5adjacent to its upstream end to the bottom of the body. Passage V185communicates with the diaphragm control chamber 37 through a hole 1857VYin the diaphragm 31, and passage 189 in the diaphragm cover 33.

Body 3 also has an inclined passage 191 extending from passage 185 tothe annular space 193 formed between nozzle 145 and the wall of aperture141. The outer end of passage 191 is closed by `a plug 195. Arestriction 199 is pressed in the lower end of passage `185below theintersectionofV passage 191. A second restriction 192 is positioned inpassage 191. Restriction 199V is'to dampen the effect of the enginepulsations in the mixture `conduit 5. f

In operation, cranking of the engine pumps air through the mixtureconduit 5 of the carburetor into the intake manifold of the engine. Flowof air past the main fuel nozzle 145 with the throttle valve 133 openprovides a subatmospheric pressure at the mouth of nozzle 145 due to theventuri effect of the restriction of throat 15. This low pressure at themouth of nozzle 145 is transferred baclr through passage 161, 143, 159,157 and 155 to the fuel chamber 29a. Lowering the pressure in chamber29a causes air pressure from passage 185 on the outer surface ofdiaphragm 31 to press the diaphragm inwardly or upwardly, as viewed inFIGURE 2, and to rock the valve lever 49 in a clock-wise direction. Thispositively pulls the needle valve 55 downwardly and the end 115 ofneedle valve olf of the resilient valve seat 107.

Pulsations in the crankcase of the engine are transferred throughpassage to the pulsation chamber 57. The pumping diaphragm 63 llexesback and forth under the effect of the engine pulsations in pulsationchamber 57. This causes a pumping action in the pumping chamber 69 whichsucks fuel from tank 51 through the conduit 78 into the inlet chamber 73of the carburetor cap 65. Fuel passes into the pumping chamber 69 andout past the outlet check valve 89 into the passages 81, 83 and 105.Continual pumping forces fuel down past the open valve into the fuelchamber 25a and out through the main fuel passage to the nozzle 145.

The capacity of the pump section of the carburetor supplies fuel at ahigher rate than used by the engine. Accordingly, fuel accumulates inthe fuel chamber 29a to lill it and the fuel reacts against thediaphragm 31 to move it outwardly against air pressure in the controlchamber 37. The valve spring 117, as the diaphragm moves away from lever49, forces the needle upwardly into a closed position in seat 107. Infuel chamber 29a, the fuel pressure within the chamber and the valvespring 117 work together against the air pressure in chamber 37 on theother surface of the diaphragm 31. The fuel pressure in the fuel chamber29a varies within a small range of values to open and close the needlevalve 55.

An idling or low speed operation of the engine takes place when thethrottle 133 is closed. At this time, there is insufficient air iowthrough the carburetor conduit 5 to pull fuel from chamber 29a throughthe nozzle 145. However, the manifold pressure downstream of throttle133 is at subatmospheric pressure and a large pressure depression iscreated at the idle jet opening 169, which pulls fuel from the fuelchamber 29a through the low speed circuit. Simultaneously sufhcient airfor mixing with this fuel and to operate the engine at low speed issucked through the idle ports 171 upstream of the closed throttle 34.This air is pulled into the idle fuel chamber 157 to mix with the fuelcoming from the fuel chamber 29a. Adjustment of screw 181 is used toprovide the optimum fuel and air mixture for idling or low speedconditions.

The diaphragm 31 and the lever 49 together with the valve 55 constitutea fuel pressure regulator such that the fuel in the chamber 29 isretained substantially at a constant pressure during engine operation.Therefore the liow of fuel through the main nozzle 145 is proportionalto the pressure differential between the fuel pressure in fuel chamber29 and the air pressure at the venturi skirt portion 15. Since the fuelpressure in chamber 29 is maintained substantially constant, thispressure differential is controlled by the iiow of air through theventuri 9 of the carburetor and is proportional to the rate of air flowthrough the mixture passage 5.

The fuel pressure in chamber 29 is determined by the balanced forces onopposite sides of the diaphragm 31. In the position of the carburetor asviewed in FIG. 2, the diaphragm assembly is pressed downwardly by theweight and the pressure of fuel in chamber 29, the Weight of thediaphragm assembly, the unbalanced weight of lever 49, the force exertedby the Valve spring 117 on needle 55 and the weight of the inlet needle55. These downward forces are balanced only by the upward pressure ofair in the control chamber 37. The air pressure in the control chamber37 is substantially that in the inlet portion of the air conduit 5 wherethe air passage 185 opens into the mixture conduit. This pressure mustbe greater than that of the fuel in chamber 29, which is determined bythe pressures created by air ow through venturi 9 or idle chamber 167.When the air filter 25 is clean, this air pressure in passage 185 isslightly less than atmospheric due to the drop in pressure caused by theslight restriction offered by the air filter 25. As the filter becomesclogged with dirt due to usage, the drop in air pressure across thefilter becomes greater so that the pressure within passage drops fartherbelow that of atmospheric. The passage 185 tends to sense the true airpressure within the entrance to the mixture conduit 5 rather thanatmospheric pressure. This drop of air pressure 'within conduit 5 isalso sensed at the nozzle 145 tending to create a greater flow of fuelout of the nozzle. However, this effect is compensated by thecorresponding drop in pressure in chamber 37 which tends to lean thefuel ow through nozzle by moving the valve 55 to a more closed position.

As the engine is operated at higher speeds with the opening of thethrottle, the static air pressure in passage 135 remains substantiallyconstant and the flow of fuel through nozzle 145 is proportional to thedrop of pressure in the venturi 9. Since at low speeds, fuel flowthrough nozzle 145 is adjusted by needle 163 to provide a relativelyrich mixture, the mixture retains its rich air to fuel ratio at higherspeeds. lt has been found advantageous to lean out the air and fuelmixture as the throttle opens from its lower speed or idle position asshown in FIG. 2. In accordance With the invention, then, the passage 191is provided between the annular space 153, formed in the surface of theventuri 9, and the air passage 155. This passage 191 permits a sensingwithin the chamber 37 of the pressure conditions in the venturi. A firstpredetermined restriction 192 is placed within the passage 191 and asecond predetermined restriction 197 is placed within pasage 15 tocontrollably adjust the pressure in chamber 37. The restriction 199enables an appropriate fraction of the venturi pressure to be sensed inthe control chamber 37 and thus to effect variations in pressure withinthe control chamber in accordance with the ow conditions at the venturi.ln this manner, the pressure in chamber 37 is reduced in proportion tothe amount of air flow through venturi 9. A drop in pressure in chamber37 as the throttle is opened up causes movement of inlet valve 55 towarda closed position to reduce fuel flow through chamber 29. The pressurein chamber 37 is thus a more accurate sensing of the engines needs andleans out the mixture ow through carburetor at speeds above closedthrottle conditions. As the throttle is moved from its wide openposition to its closed position, the venturi pressure in the skirtregion 15 increases a corresponding amount and is sensed through passage191 in chamber 37 to enrichen the air and -fuel mixture ratio,accordingly. With closed throttle and with a no flow of fuel through theventuri, the passage 191 shows little or no difference in pressure fromthat in passage and accordingly is thus not eifective during thiscondition of engine operation.

Therefore, in accordance with the invention there is provided amodifying passage 191 connecting the control passage 185 of chamber 37with the venturi skirt surface 15. As described above, this provides aproper sensing of the pressure conditions adjacent to the nozzle 145 sothat the same pressure acting on the nozzle 145 to draw fuel through themain fuel passages is also operative to control the pressure withinchamber 37 and thus modify the fuel flow through nozzle 145 according tothe changes in engine operation. Thus, instead of controlling theoperation of the diaphragm 31 only by the static pressure air/4free Y atthe entrance to the mixture conduit immediately adjacent to the airfilter 25, an additionalvcontrol is used to provide a signal whichsenses the ,pressure conditions at the nozzle 145. This reflects moreaccurately the pressure conditions in the venturi which are operative onthe nozzle and provides Va more optimum air/fuel mixture during allconditions of engine operation. i

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions Withoutdeparting from the scope of the invention, it is intended that a-llmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitM ingsense.

What is claimed is:

l. A carburetor comprising a body, a fuel and air mixture conduitthrough said body, said body formed with a fuel chamber, said mixtureconduit having an inlet and an outlet and a restricted portionintermediate said inlet and outlet, a fuel inlet and a fuel passageextending from said fuel inlet to said fuel chamber, an inlet valve insaid fuel passage between said fuel inlet and said fuel chamber, a mainfuel nozzle within said conduit restricted portion, said body having anannular space around the nozzle openinginto said restricted portion,said body having a fuel connection from said fuel chamber to said mainfuel nozzle, means for operating said inlet valve, said operating meansincluding a diaphragm operatively connected to said inlet valve andsealed at its periphery to said body across said fuel chamber to form aWall thereof,

. 8 4 f. spring means biasing said inlet valve in a valve closingdirection and said diaphragm in a direction to enlarge said fuelchamber, means forming la single closed air chamber enclosing the sideof said diaphragm opposite to said fuel chamber, said bodyV including afirst passage connecting said mixture conduit inlet to said air chamberwhereby said diaphragm is responsive to conduit inlet airV pressure tomaintain fuel in said fuel chamber at a constant pressure, and a secondpassage in said body interconnecting said annular space and said firstpassage whereby said diaphragm is responsive to the drop in air pressureat said conduit restrictive portion to vary the constant` pressure offuel in said fuel chamber directly in response to changes of airpressure at said nozzle.

2. A carburetor as set forth in claim 1 wherein said second passage has`a restriction therein.

3. A carburetor asset forth in claim l wherein said first passage has arestriction therein between said second passage and said inlet.

References Cited by the Examiner UNlTED STATES PATENTS HARRY B.THORNTON, Pinmry Examiner.

HERERT L. MARTN, Examiner.

1. A CARBURETOR COMPRISING A BODY, A FUEL AND AIR MIXTURE CONDUITTHROUGH SAID BODY, SAID BODY FORMED WITH A FUEL CHAMBER, SAID MIXTURECONDUIT HAVING AN INLET AND AN OUTLET AND A RESTRICTED PORTIONINTERMEDIATE SAID INLET AND OUTLET, A FUEL INLET AND A FUEL PASSAGEEXTENDING FROM SAID FUEL INLET TO SAID FUEL CHAMBER, AN INLET VALVE INSAID FUEL PASSAGE BETWEEN SAID FUEL INLET AND SAID FUEL CHAMBER, A MAINFUEL NOZZLE WITHIN SAID CONDUIT RESTRICTED PORTION, SAID BODY HAVING ANANNULAR SPACE AROUND THE NOZZLE OPENING INTO SAID RESTRICTED PORTION,SAID BODY HAVING A FUEL CONNECTION FROM SAID FUEL CHAMBER TO SAID MAINFUEL NOZZLE, MEANS FOR OPERATING SAID INLET VALVE, SAID OPERATING MEANSINCLUDING A DIAPHRAGM OPERATIVELY CONNECTED TO SAID INLET VALVE ANDSEALED AT ITS PERIPHERY TO SAID BODY ACROSS SAID FUEL CHAMBER TO FORM AWALL THEREOF, SPRING MEANS BIASING SAID INLET VALVE IN A VALVE CLOSINGDIRECTION AND SAID DIAPHRAGM IN A DIRECTION TO ENLARGE SAID FUELCHAMBER, MEANS FORMING A SINGLE CLOSED AIR CHAMBER ENCLOSING THE SIDE OFSADI DIAPHRAGM OPPOSITE TO SAID FUEL CHAMBER, SAID BODY INCLUDING AFIRST PASSAGE CONNECTING SAID MIXTURE CONDUIT INLET TO SAID AIR CHAMBERWHEREBY SAID DIAPHRAGM IN RESPONSIVE TO CONDUIT INLET AIR PRESSURE TOMAINTAIN FUEL IN SAID FUEL CHAMBER AT A CONSTANT PRESSURE, AND A SECONDPASSAGE IN SAID BODY INTERCONNECTING SAID ANNULAR SPACE AND SAID FIRSTPASSAGE WHEREBY SAID DIAPHRAGM IN RESPONSIVE TO THE DROP IN AIR PRESSUREAT SAID CONDUIT RESTRICTIVE PORTION TO VARY THE CONSTANT PRESSURE OFFUEL IN SAID FUEL CHAMBER DIRECTLY IN RESPONSE TO CHANGES OF AIRPRESSURE AT SAID NOZZLE.